1. Field of the Invention
This invention relates bag filters and their mountings for filtering return air of a forced air furnace system, with the return air duct as the housing for the system.
2. Prior Art
Return air filters for residential and commercial forced air heating and cooling units have traditionally been installed in the transition between the air handler and the termination of the return air duct. This tradition is typically a one inch filter rack installed between the air handler and the end of the duct, or inside the air handler, or some higher efficiency filters supply their own housing to hold their filter, which is installed between the air handler and the termination of the return air duct, which requires modification of the duct to allow for the housing to fit into the system.
Return air filters for residential and commercial forced air furnaces have traditionally employed square or rectangular filters having an outer frame formed from cardboard, or the like, that hold an air filtration material, such as fiber glass, or a more efficient material, across the frame. Some higher efficiency filters have been developed which are four to twelve inches thick, using material that is pleated from one inch to six inches and require major adapting of the return air duct in order to use these types of filters. Where such filter material is efficient for removing particles from an air flow, including some very small particles, it is less efficient and useful than the filter material preferred for the invention, as has been developed for use as the bag material of the invention that is known as a high efficiency bag air filter (HEBA™) that effectively removes particles from the inlet air flow to an air handler and has more surface area in the filter, without clogging as quickly as filters of less surface area could experience. In practice, the filter material of the invention has been found to last longer than conventional filters because of the increased surface area of the filter.
Previous higher efficiency furnace filters have required the modification of the return air duct of the heating and cooling system. The invention can be easily installed from the front of the duct by cutting a single hole in the duct, installing an access door onto the outside of the duct and a rail inside the duct for the filter assembly to rest on and the other side of the assembly rests against the opposite side of the duct. Thus, eliminating the need for extensive and expensive remodeling of the return air duct.
Unlike earlier filtration arrangements that employ flat elements or pleated filter media, the air filter system of the invention provides the inner surface of each of an optimum number of bags for the furnace duct interior dimensions as the air engages surfaces. Accordingly, the filter system provides an improved capacity for return air filtration over a longer period of time than has been possible utilizing a single flat filter only or even a pleated type filter. Where, of course, bag filters have been in use in industrial applications, such as power plants, they have not been incorporated into residential furnace systems. Nor have such earlier uses involved a unique and practical bag mounting and installation system like that of the invention.